As is known, self-clocking glyph codes are suitable for embedding machine readable data in images of various descriptions, but they are especially advantageous for applications that require or benefit from having the machine readable data embedded in the images in a visually nonobstructive or aesthetically pleasing way. Specifically, to provide a visually homogeneous glyph pattern (a glyph pattern in which the glyphs are substantially indistinguishable from each other when viewed by the naked eye under normal lighting conditions) all of the glyphs of the self-clocking glyph pattern typically are defined by symbols from the same symbol set, such as slash-like symbols that are tilted from vertical at approximately .+-.45.degree. to encode binary "0s" and "1's," respectively. More generally, however, a "glyph" is any optical character that has at least two graphical states for encoding at least two logic states ("1" and "0") of a single bit.
A self-clocking glyph pattern comprises data glyphs that encode information of user interest and reference glyphs that encode overhead information, such as spatial synchronization, address information, labeling information and authentication. This overhead information facilitates the reading and/or interpretation of the data glyphs. Typically, data glyphs are arranged in a two-dimensional lattice. Reference glyphs may also take on a two-dimensional lattice configuration. For example, U.S. Pat. No. 5,449,895, entitled "Explicit Synchronization For Self-Clocking Glyph Codes," gives a number of examples of data glyphs, reference glyphs, and lattice structures.
In general, many of the applications for two-dimensional reference glyphs codes interleaved with data glyph codes involve synchronization of glyph codes. U.S. Pat. No. 5,449,895 for example, deals with facilitating robust synchronization of glyph codes This patent also cites useful background references on self-clocking codes and related applications. The contents of U.S. Pat. No. 5,449,895 is hereby expressly incorporated herein by reference.
U.S. Pat. No. 5,576,532 entitled, "Interleaved and Interlaced Sync Codes and Address Codes for Self-clocking Glyph Codes," describes self-clocking reference glyphs interleaved or interlaced in two dimensions with data glyphs to facilitate the partitioning and correlation of data embedded in the data glyph codes. Specifically, with respect to FIG. 4 there is disclosed the mapping of interwoven two-dimensional interleaved reference glyph codes with data glyphs into a self-clocking glyph code pattern.
Thus, the '531 patent discloses interleaved self-clocking glyph codes to facilitate the partitioning and/or correlation of data subsets based on local spatial relations of reference glyphs in a data glyph code pattern. This approach can improve the interpretation of the logical relationship among data sets and the data in each data set. Both one-dimensional and two-dimensional linear subarray interleaving is described. The contents of U.S. Pat. No. 5,576,532 is hereby expressly incorporated herein by reference.
The present invention builds on and extends the techniques disclosed in U.S. Pat. Nos. 5,449,895 and 5,576,532.